Organic electronic devices using organic semiconductive materials have been actively studied in recent years. The organic semiconductive materials can be formed into a thin film by a simple wet process, such as printing and spin-coating. Therefore, they have advantages over electronic devices using the conventional inorganic semiconductive materials, such as the reduction in temperature for production processes and in cost. Since use of the organic semiconductive material can reduce the temperature of the production processes and cost, the thin film thereof can be formed on a plastic substrate which has generally low heat resistance. As a result, weights or costs of resulting electronic devices such as a display can be reduced, and various uses and applications thereof taking advantage of flexibility of a plastic substrate can be expected.
Some organic semiconductive materials have been proposed so far, such as poly(3-alkylthiophene) (see NPL 1), and a copolymer of dialkylfluorene and bithiophene (see NPL 2). Since these organic semiconductive materials have some solubility to a solvent, though it is low, they can be formed into a thin film by coating or printing without using a technique such as vacuum deposition. However, these polymer materials have restrictions in their purification methods. Therefore, some problems still remain. For example, it is complicated and time consuming to obtain a material of high purity, and quality of the material is not stable as there are variations in molecular weight distribution thereof.
On the other hand, low-molecular-weight organic semiconductive materials have also been proposed, such as acene materials (e.g. pentacene) (for example, see PTL 1). It has been reported that the organic thin film transistor including an organic semiconductive layer formed of the pentacene has relatively high electron mobility. However, these acene materials have extremely low solubility to common solvents. Therefore, these materials need to be vacuum-deposited to form a thin film thereof as an organic semiconductive layer of an organic thin film transistor. Moreover, such organic thin film transistor has poor atmospherical stability. For this reason, these materials do not meet the demand in the art, which is to provide an organic semiconductive material that can be formed into a thin film by the aforementioned wet process such as coating or printing.
Moreover, there are some reports regarding low-molecular-weight organic semiconductive materials that have solubility to solvents. However, these materials still have problems. For example, a film formed of such material by a wet process is in the state of amorphous, and thus it is difficult to form a continuous film using such material due to crystal properties of the material. Moreover, suitable characteristics of the film cannot be obtained using such material. Therefore, the development of the novel organic semiconductive materials which can be processed by a wet process, such as printing is still strongly demanded.